Aluminum-boron carbide (ABC) composites are of interest for components, such as computer hard drive disks, because of their lower density and higher stiffness than aluminum metal. One of the most desirable methods of forming complex shapes of aluminum-boron carbide composites has been to infiltrate a boron carbide preform with aluminum. The infiltration method results in a dense ABC composite having essentially the same geometry and dimensions as the porous preform.
Unfortunately, because aluminum metal has an aluminum oxide layer, infiltration has to be performed at a high temperature (i.e., above 1000° C.). Thus, infiltration has required the use of preforms that are self-supporting. This has precluded the use of substantial amounts of aluminum in the preform. This is because the preform slumps and incompletely infiltrates due to melting of the aluminum in the preform and sintering and reacting with the boron carbide causing the pores to be closed off from the infiltrating metal. Consequently, infiltrated ABC composites have been limited to high boron carbide concentrations (i.e., at least about 40 percent by volume). The lower limit for a self-supporting porous particulate body is generally considered to be 40 percent particulates and the balance pores.
Other techniques have been used to form ABC composites with high aluminum concentrations, such as solid state sintering and high pressure techniques below the melting temperature of aluminum. However, sintering at temperatures below the melting temperature of aluminum suffers from sintering shrinkages resulting in costly machining and, consequently, only making simple shapes economically viable. Similarly, high pressure techniques, such as extruding aluminum and boron carbide, are expensive and limited in the shapes that can be made. In addition, since the aluminum does not melt in these techniques, the bonding between the boron carbide is substantially less compared to when the aluminum melts and reacts with the boron carbide. Consequently, a composite with less than optimal properties is formed by these techniques.
In addition, boron carbide has been cast in molten aluminum, but since boron carbide reacts quickly with molten aluminum and decomposes into boron metal, carbon and water soluble aluminum carbide, the boron carbide is first encapsulated with a protective metal, such as silver. These techniques suffer from the inability to control detrimental phases that reduce strength (e.g., Al4C3) in the absence of an additional expensive step of coating the boron carbide prior to casting. This protective layer precludes the boron carbide to interfacially bond (react) with the aluminum to make, for example, a stronger composite.
Accordingly, it would be desirable to provide a material and method that overcomes one or more of the problems of the prior art, such as one of those described above.